It's the other way round. The first part isn't true - the bank doesn't buttonhole some saver into giving them a few hundred grand when you take out a mortgage.

It's the other way round. The first part isn't true - the bank doesn't buttonhole some saver into giving them a few hundred grand when you take out a mortgage. (It might get the deed to your house, physically or metaphorically - but there are also unsecured loans). The second part is true: when you make a deposit the bank has some more cash and will surely invest it/loan it out/deposit it at another institution. Those three phrases all mean roughly the same thing: the bank will take the pile of copper and linen you gave it and use it to purchase another asset.